Jewish War Veterans of the USA National is our umbrella organization. They speak for all membership. Members join a Post, normally based on geography (closest to where they live). Many Posts report directly to National with no intermediate levels.
In some areas of the country, there are enough multiple Posts close enough together that they form a Department to consolidate functions, such as fund-raising, publicity, and recruitment. Also to coordinate with outside organizations that need to communicate with JWV about parades and other events. Where there is a Department, it acts as an umbrella organization over the Posts. Although Posts do still have some autonomy, they are obligated to coordinate with the Department.
In Michigan, we have three Posts in the metro-Detroit area: Lt Raymond Zussman (CMH) Post 135, PFC Joseph L Bale (DSC) Post 474, and Charles Shapiro-MG Maurice Rose Post 510. The JWV Department of Michigan represents them all. Officers and members from the three Posts serve on the Executive Committee of JWV Department of Michigan. These Posts used to geographically cover different areas, however, that changed when the Oak Park JCC was closed. Prior to the closing, Post 135 met in the Oak Park JCC, Post 510 met in Southfield, and Post 474 met at the West Bloomfield JCC. Department leadership decided to consolidate all three meetings into the West Bloomfield JCC and have them at the same time to improve communication; they added a first-ever "department-wide" meeting following the separate Post meetings.
However, the West Bloomfield JCC had a problem - it was too far from the parking lot (even handicap parking) to the meeting area. Some members in wheelchairs or with walkers couldn't handle it. So we switched meeting locations to Temple Shir Shalom in West Bloomfield.
Since we all meet in the same location at the same time in separate corners of the Temple Shir Shalom social hall, which Post you join really is not a geographic decision anymore. Now, it is usually based on whether you know someone else (which Post are they in) or which Post is the least-populated. As of June 2019, our three Posts range in size from 55 to 75 members.